One of the most severe safety problem encountered in high power multi-cell batteries is thermal runaway during accidental short-circuit of a single cell in the battery. In order to avoid such a case all high power lithium batteries (and also many other batteries) are equipped with a pressure release vent in addition to a fuse. However, the release to the surroundings of toxic and corrosive materials is thus not avoided. The major problem is that the heat capacity of a single cell is too small to avoid dangerous overheating.